Illegal immigrants reportedly assaulted two U.S. Border Patrol agents with rocks, killing one and seriously injuring another Sunday near the southern border with Mexico. Details around the attack remained murky Monday, however, an FBI spokesperson said Rogelio Martinez and his partner were not shot and a National Border Patrol Council official told KTSM the assailants were "undocumented immigrants" who used likely used rocks to bash the agents. "We strongly believe rocks were what was used," NBPC Vice President Art Del Cueto told KTSM. The FBI had taken over the investigation into the death of Martinez, 36, and the injuring of his partner, who was not identified.